OUTGOING NEUTRONS IN CALET CALET AIMS AT DETECTING UHE CR ELECTRONS HIGH REJECTION FACTOR FOR PROTONS/NUCLEI NEEDED POSSIBLE IMPROVEMENT RESPECT ‘STANDARD’ CALET :  DETECT NEUTRONS ASSOCIATED TO SHOWERS  DIFFERENT NUMBER OF OUTGOING NEUTRONS ARE EXPECTED FOR HADRONIC AND PURE ELECTROMAGNETIC SHOWERS

FIRST STEP : EVALUATE THE NUMBER AND PHENOMENOLOGY OF OUTGOING NEUTRONS BY MEANS OF SIMULATION SIMULATION LIBRARY : FLUKA ( very reliable for hadronic simulation ) FLUKA CONTAINS THE PHYSICS OF NEUTRON PRODUCTION BY PROTONS AND ELECTRONS : physics reliability to be investigated further THE GEOMETRY AND MATERIALS OF CALET ( IMC+TASC ) HAVE BEEN PLUGGED INTO FLUKA MATERIALS BUT NOT DETECTORS ARE SIMULATED FOR IMC MATERIALS AND DETECTORS ARE SIMULATED FOR TASC

CALET FLUKA SIMULATION PROTONS AND ELECTRONS ARE SIMULATED IN FULLY ANALOGUE APPROACH FOR EACH EVENT ARE SAVED IN OUTPUT :  ENERGY LOSS IN EACH BGO BAR ( X AND Y )  INDIVIDUAL NEUTRONS (ENERGY,TIME,POSITION, DIRECTION..) EXITING FROM THE SIDE AND BOTTOM SURFACE OF TASC  POSITION ( IMC OR TASC ) OF THE FIRST INELASTIC NUCLEAR INTERACTION AS STARTING APPROACH WE SIMULATED PROTONS AND ELECTRONS WITH FIXED ENERGY DIRECTED VERTICALLY AND EXACTLY IN THE CENTER OF THE APPARATUS P,e Bottom detectors ? Side detectors ? (low energy neutron emission is isotropic)

CALET FLUKA SIMULATION 1TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons IN THE FOLLOWING WE SELECT ALWAYS ‘INTERACTING’ PROTONS AS THOSE WHO HAVE AN INELASTIC NUCLEAR INTERACTION ABOVE TASC (IN IMC ) 1 TeV protons 400 GeV electrons

CALET FLUKA SIMULATION What about outgoing neutrons ? ENERGY SPECTRUM OF OUTGOING NEUTRONS (side+bottom) 1 TeV protons Peak of excited nucleus emission Direct neutrons emission in hadronic interactions plus multiple neutron reinteraction ? Direct neutrons emission E<1 MeV 60% 400 GeV electrons E<1 MeV 87% 1TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons

ENERGY SPECTRUM OF OUTGOING NEUTRONS (only side) 1 TeV protons The ‘direct’ contribution is absent (as expected) ENERGY SPECTRUM OF OUTGOING NEUTRONS (only bottom) 400 GeV electrons E<1 MeV 70% E<1 MeV 54% E<1 MeV 87% E<1 MeV 87%

What about outgoing neutrons ? ARRIVAL TIME (SIDE+BOTTOM) 1 TeV protons The low energy neutrons arrive later respect to the high energy and to the expected arrival of charged component of the shower (nanoseconds) 1TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons

400 GeV electrons

What about outgoing neutrons ? NUMBER OF NEUTRONS (SIDE+BOTTOM) (approx. proportional to the energy of the primary) 1 TeV protons 400 GeV electrons MORE THAN A FACTOR 10 !!! BUT TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons

What about outgoing neutrons ? NUMBER OF NEUTRONS (SIDE ONLY) 1 TeV protons 400 GeV electrons MORE THAN A FACTOR 10 !!! BUT TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons

What about outgoing neutrons ? NUMBER OF NEUTRONS (BOTTOM ONLY) 1 TeV protons 400 GeV electrons MORE THAN A FACTOR 10 !!! BUT TeV proton has in TASC similar averaged amount of energy released respect to 400 GeV electrons

ARRIVAL TIME OF PARTICLES ON THE NEUTRON DETECTOR (normalized to one event) – Only Bottom – Interacting on IMC (no selection) 64% of neutrons arrive after 10ns 40% of neutrons arrive after 30ns N  charged 1 TeV Proton showers

NEUTRONS ARRIVAL TIME FOR 3 SINGLE P EVENTS EVENT 1 EVENT 2 EVENT 3

charged N  ARRIVAL TIME OF PARTICLES ON THE NEUTRON DETECTOR (normalized to one event) Only Bottom 400 GeV electron showers

REJECTION IN CALET 10^5 PROTONS WITH 1 TeV simulated isotropically (76389 in the strict acceptance with all the 12 planes hitted. As used for this simu) 500 ELECTRON WITH 400 GeV simulated isotropically (375 in the strict acceptance with all the 12 planes hitted. As used for this simu) PROTONS WITH FIRST INTERACTION BELOW IMC REJECTED According to CALET papers ( see 2003 ICRC presentations) FOR EACH X AND Y PLANE OF THE TASC THE FOLLOWING VARIABLES ARE CALCULATED : Efrac=Energy in the plane / energy in the calorimeter rms = (rms of the energy deposition in the plane respect to axis) / 0,25cm Fvalue = Efrac*rms^2 12 (6 x and 6 y ) BGO planes with 2,5x2,5 cm^2 bars

rms Efrac Distribution for the last (12th) plane : according to calet declared rejection we expect less than 1 event contaminating the electron region, we see around 10 irreducible events protons electrons

Fvalue(12) Fvalue(11) Using these cuts : 70% efficiency (electrons) 7,6*10^3 rejection factor If we select only protons releasing more than 400GeV in the TASC we have a rejection of 2*10^4 Cutting on Fvalue MUCH WORSE THAN CALET CLAIM

DOES NEUTRONS HELP ? Number of neutrons exiting from below Protons interactiing in IMC electrons Protons interacting in IMC Plus cuts on Fvalues Electrons with cuts on Fvalues

NORMALIZING THE NUMBER OF NEUTRONS WITH ENERGY RELEASED Electrons after the cuts Protons after the cuts Neutrons can improve the rejection by a factor around 1,5 ? Neutrons/Ecal

38000 PROTONS WITH 5 TeV simulated isotropically (29000 in the strict acceptance with all the 12 planes hitted. As used for this simu) 500 ELECTRON WITH 2 TeV simulated isotropically (383 in the strict acceptance with all the 12 planes hitted. As used for this simu)

Distribution for the last (12th) plane Efrac rms

10^5 proton at 1 TeV 4*10^4 proton at 5 TeV rms Efrac

Fvalue(12) Fvalue(11) Cutting on Fvalue Electron Efficiency 76 % Nsimulated/Nselected=6*10^3

Neutrons/Ecal After the cuts